High-performance polyethylene separators for lithium-ion batteries modified by phenolic resin

In lithium-ion batteries, separator serves to isolate the positive and negative electrodes, as well as provide a free shuttle for Li-ion transport inside the battery . Commercial polyolefin separator has relatively higher thermal shrinkage and lower electrolyte wettability , which limits the application of batteries in extreme conditions. In this work, we prepared phenolic resin (AF) modified polyethylene (PE) composite separators by the process of immersion in situ reaction. The obtained PE@AF composite separator has lower thermal shrinkage and higher electrolyte wettability than pure PE separator. The shrinkage of our prepared PE@AF separator is only 6% when stored at 145 °C for 30 min, greatly smaller than the pure PE separator (more than 77%). Moreover, the ion conductivity of PE@AF composite separator increases from 0.206 mS cm −1 for the pure one to 0.604 mS cm −1 . Apart from this, the Li/electrolyte-soaked PE@AF separator/LiFePO 4 battery exhibits a higher coulombic efficiency (96.7%) and discharge capacity retention rate (86.0%) after 450 cycles than the pure one (67.4% and 72.7%, respectively). Our results indicate that the AF coating plays a vital part in improving the thermal stability and electrochemical property of polyolefin separators.